In the U.S., the word "trailer" can refer to a towable recreational vehicle used for part-time leisure occupation and to a manufactured home -- designed with wheels and a tow hitch intended for delivery only -- that is used for full-time occupation. The latter construction most often is elevated onto concrete blocks. However, because the RVs are universally smaller, the processes for lifting the homes can apply to them also.
Ensure no local codes require inspection of the site, tie-downs, support pads or permanent utility provision. Ensure that there are no maximum or minimum square-footage regulations to be adhered to. Some insurers require that trailers they cover only be elevated by bonded professionals.
Chock the wheels of the trailer so that it absolutely cannot move. Very infrequently, older models can be found with a hand brake lever -- similar to emergency brakes on European cars -- attached to the tongue. If such a device exists, deploy it. If blocking up a towable RV that has electric brakes, connect the circuit directly to the poles of a fully-charged car battery. This will fully deploy the electric brakes. Check through the interior of the trailer to ensure all closet and cabinet doors are latched securely, and that nothing loose is likely to move or suffer damage when the angle of the floor is moved conspicuously off horizontal. Look above the trailer to ensure no low-hanging branches or utility wires could be contacted by the operation. In the case of the latter, call the utility company to have the wires adjusted. Ensure that the ground below the trailer is sufficiently solid to take the weight of the entire construction when it is transferred through the pilings. If necessary, lay support slabs. Measure the height of the trailer chassis from the ground, and calculate the height that the block pilings will need to be to lift the wheels clear.
At no point during the operation should anyone either enter or go beneath the trailer.
The Seesaw Method
Lowering the tongue raises the rear of the trailer. Drop the tongue far enough to increase the distance between the rear end and the ground sufficiently to accommodate the block pilings. If dropping the tongue to the ground does not create such a gap, dig out a trench into which the tongue can descend temporarily for this part of the operation. The weight-bearing block pilings must be built close to the axles, under the part of the chassis designed to take the construction's weight, not at the outside corners. Outside corner pilings act only to steady the trailer. Each of the eight pilings -- two at each outside corner, and two aft and two fore of the axles -- must have a hardwood panel that slots between the blocks and the metal of the chassis.
Build the Rear Block Pilings
Build two block pilings, one under each side just aft of the axles. Arrange the blocks so that their sides and the central membrane are horizontal at right angles to the ground. Each course must consist of two blocks laid side-by-side. Lay the first course in one direction, and the second in the opposite direction, so that one long side is visible in the first course and two short sides are visible in the second. The edges must be square with the edges of the trailer chassis. Build the pilings to the predetermined height. Insert the hardwood panels.
Rest the Trailer on the First Pilings
Raise the tongue using a 20-ton heavy-duty automotive jack of the piston (bottle) variety, not of the scissor variety. If raising an RV trailer, do not use the integral tongue jack -- it is unlikely to be designed to take the torsion strain or be long enough -- but use an automotive jack. Do not use two smaller jacks at each front corner as this practice can wring the trailer, and cause problems, such as water leaks and jammed doors. Raise the tongue until the rear part of the chassis settles onto the pilings. Continue raising the trailer until the front end is above horizontal from the rear end, which lifts the wheels off the ground. Repeat the block piling installation, this time with two pilings just fore of the axles. Lower the jack so that the trailer rests on all four pilings. If the trailer floor is off level, slightly raise or lower the tongue and insert hardwood shims above either the front or rear pilings to level off the chassis.
Build Corner Pilings
Install pilings under each outside corner using the same structural patterns as before. If there is not enough room to fit full blocks under the chassis, alter the ground level to accommodate them. If they are slightly short, tap in hardwood shims.
It is advisable to surround the void beneath an elevated trailer with a breathable barrier, such as proprietary latticework or chicken wire, to exclude pests. If the location is susceptible to extremes of heat or cold, seal the void with heavily insulated material. After six weeks, recheck level. If any settling has occurred it is important to rectify the discrepancy for the aforementioned reasons.