One of the first things to do when you get to camp is to level out the rig so that it is comfortable to live in and the appliances work properly. Trailers are fairly easy to level as you only have to ramp up one side or the other and then can use the tongue jack for front to back adjustments. Motor home leveling is a bit more complex as you might need to ramp up three wheels.
This surface needed a lot of adjusting! Note the step to help trailer access.
There are two standards for determining how level is level enough for an RV. One is whether it is comfortable - you don't slide out of the bed; food doesn't slide out of pans when trying to cook, you don't feel like a sailor in a rough sea trying to stay upright when walking down the hall. The other standard is to make the rig level enough to be able to operate the refrigerator properly.
In order to assure proper operation of the RV refrigerator the rig should be no more than a half bubble on the level off. This is about two degrees or an inch off level per three feet or about a 3% grade. For a 25' trailer that is 7' wide, this means the hitch jack can be up to 4 inches too far up or down and one side can be a bit more than two inches higher than the other. If you are so far off level as to be in this borderline state, the odds are that you won't be very comfortable inside the rig, either.
You level the rig side to side by adjusting the surface. You do not level the rig by using jacks unless you have special jacks specifically designed for lifting and holding the rig. The only jack used for leveling trailers is the tongue jack for front to back leveling. To level side to side, ramps are used to drive the tires up on blocks.
When you make or purchase blocks and ramps for leveling your vehicle, first measure the footprint of your tires so you can be sure that the tires can sit completely on the blocks and ramps with full support.
The first ramps and blocks most people use are crafted from common lumber. One source is (with permission, please) the waste pile from a construction site. Others buy a stick from a local lumber yard. The most common lumber is probably the 2x6 although a 2x8 or 2x10 may make getting a full footprint easier. The 'two-by' lumber will raise one side of the trailer by a bit over one degree so a stack of 2 - 3 boards is often needed. Lumber is relatively inexpensive and can provide good load distribution to prevent sinking in loose soils. But lumber is also heavy, tends to crack, can be dangerous to stack, may be difficult to clean and store, and may slip when you use them on some surfaces or when stacking.
At least two companies make plastic interlocking blocks designed to help RV leveling. A set of ten of these often comes in a zippered bag and costs about $40. A set can raise one tire about two or three inches in a pyramid stack. These are convenient, lightweight, easy to store and clean, and very rugged. You can find them in most RV supply stores.
In addition to blocks that can be assembled for a desired lift height, there are ramps such as the EZ-Jack and Tri-leveler that are pre-built ramps. On these you just move the trailer up the ramp until it is level (assuming that it can be made level within the rise available with the particular ramp). You can make something similar to these ramps by fastening together a collection of boards.
On any of these ramps and blocks schemes, you will need to consider the distance between tires if you have tandem axles on your trailer. It is generally best to lift both tires on one side of the trailer so you will need at least two of each item and your ramp and block system will need to fit on the ground between the tires.
Always try to drive forward at idle speed to move the trailer up on ramps and make sure no one is in a position to get hit by 'squirting' blocks or ramps squeezed out from under the wheels. Most transmissions provide a bit better or lower forward gearing and it is easier to watch out for hazards going forward. If you have enough slope to the rear to make it easier to back onto the ramp, you probably won't have room to lower the tongue enough to get level front to back.
Chock the wheels firmly! This is not only a safety measure but also reduces movement of the trailer as you walk around. Only unhitch your trailer after you have it leveled side to side and secured with chocks. You need to chock both sides to prevent not only back and forth movement but also any rotations about the wheels on one side. With tandem wheels you can purchase or make a device that fits between the wheels and wedges against the tires to prevent movement (see photo).
After you have the rig level and secured, then set up the stabilizing jacks. These are usually positioned near each corner of the rig at a spot where they have good frame contact. They should be set tight but should not be used for any lifting duty. The purpose of these jacks is to reduce movement and not to change the attitude of the rig. A common stabilizing jack is shown in the photo. There are also scissors type jacks that mount to the trailer.
The simplest way to determine if your rig is level enough is to go inside, walk from one end to the other, sit on the toilet, and put something round like a fruit on the counter. If you like a bit more than this, there are all sorts of products available to help you out. There are some levels that are large enough to see in the rear view mirror. There are others calibrated to tell you how many inches to raise one side or the other to get to level. You can also use standard levels from the pocket pencil type to full blown carpenter's level to see how close to perfection you have your rig.
The one level everyone should have is a round button type. These are about an inch in diameter and measure both front to back as well as side to side level at the same time. They are very handy to set in the refrigerator for a quick level check. Make sure the bubble is at least halfway inside the indicator circle when it is set on the floor of the freezer compartment, which is solidly attached to the frame on three sides.
When measuring level, you need to calibrate your measuring point. The best reference to use is usually the freezer floor in the refrigerator (Make sure you have bare metal to sit the level on so frost or whatever doesn't warp the measure.). If everything is built to kilter, a level in the refrigerator will match one on the floor, counter, or bumper - but this isn't always the case so check a convenience reference point so you know its bias, if any. Permanently mounted levels will have adjustments to make it possible to have them read the same as a reference level. Whenever you use a level, make sure it is solidly mounted out against a flat surface. A level on a nice plush carpet on the floor is not a good way to make a good measurement. Having one end of a level sit on a bolt on the bumper will also throw off results.
Use ramps and blocks for side to side leveling
Chock both sides before loosening the hitch
Stabilizing jacks are not for lifting
Always check to see that jacks are removed before moving the rig
Check the camp when leaving to make sure you didn't leave anything behind.