Foundation for semi-permanent RVedited by Tom Jones
We were asked about the best kind of foundation for a 5th wheel that will be used as a semi-permanent home. The following is a compilation of suggestions from forum members and staff, most of it based on personal experience of the posters. Several of these options would also work for long-term parking of a motorhome.
A reinforced concrete pad over baserock provides the most permanent solution, although this may not be the best option for all soil conditions and is difficult/expensive to remove if you change your mind later.
Baserock from a landscape yard would work as a temporary base. Use maybe 8" and it will compact pretty good and be a decent temporary base. But check with a local landscape service for recommendations specific to the soil conditions.
Local stone will work for a temporary foundation. Put down plenty of a large size stone (e.g cobblestone) to support the weight.
A fifth wheel could be set up on concrete (or cinder) blocks in the manner used for most mobile homes. It you use enough of them and take care leveling, you should have a solid, yet easily moved foundation. Use double columns at the corners and a columm somewhere in the middle of each side, about where the axles are. Use stone or baserock under the concrete blocks to help drainage and prevent the blocks from sinking. If you mount the trailer using this method, take the wheels off and store them inside, out of the direct sunlight. This will greatly reduce the rate of oxidation of the compounds in the tire rubber. Then you'll be less likely to have a tire problem when you want to move it in the future. Alternatively, since the tires will need replacing in 5-7 years, even if unused, sell them while they still have some value.
A fifth wheel will have "landing gear" in the front, which are adequate for fairly long term support, but still reinforce the front corners with blocks to take most of the weight. Keep the front up in case the front hydraulics ever fail. It may also be a good idea to support the king pin (the hitch under the front) to reduce vibration and the tendency to sway slightly.
If the trailer is standing on its wheels and front jacks you will probably want a king pin jack to firm things up. They sell specialized portable bipod or tripod jacks for this, but you can jury rig something if you plan for a permanent foundation later. The ubiquitous concrete block colum (at least double blocks, because it is tall) probably would work with a little scissor or bottle jack added at the top.
In areas prone to high winds, use metal strap tie downs to make sure the RV stays on the foundation. Check with local building suppliers for tie downs and anchors for portable building (if local codes allow them at all). If there is enough soil you may be able to use giant screws (10 inches wide and 4-5 fet long) as anchors.
Another option that might be helpful in distributing the weight over a large area is Perforated Steel Plate over a bed of crushed stone or pea gravel.
Contributors to this article were Gary Brincks, Tom Jones, Karl Kolbus, Carl Lundquist, Bob Maxwell and Chet Parks.