Regarding insulation…our manager at our community in Minnesota “commandeered” some 2" rigid foam scraps and positioned them behind the vinyl skirting, between the underside of the home and the ground all around the inside perimeter and then installed a radio frequency thermostat and monitored the temperature for one winter. The temperature never fell below freezing that winter with the insulation. Slowly, (and usually after a winter freeze-up) our other residents started copying what my manager did. This 2018-19 winter has been below zero for more days than I can count and (knock on wood) we have had no freeze-ups with the exception of a couple of residents not confirming the heat tape around the water meters was turned on. The material is very similar to this: https://www.homedepot.com/p/R-Tech-2-in-x-4-ft-x-8-ft-R-7-7-Rigid-Foam-Insulation-310891/202532856
Regarding the slabs: Over ten (10) year period, we now have almost all the homes on slabs. We increased the rent $100/month for homes on slabs and the break even is about 5-6 years. Minnesota is already highly regulated in manufactured housing and not long after we purchased the community, the laws in Minnesota became more strict regarding installs with newer homes and/or older homes moving around. What I did was read the installation requirements from as many manufacturers as I could find coupled with HUD install requirements and drew up my own slab that would (hopefully) meet or exceed any manufacturers specifications. It has extra rebar in it so the slabs can accommodate 14 or 16 foot wide homes.
Here is what I can tell you about slabs. They do float and move around, but the great thing about slabs is the whole house moves with the slab. If you use any other type of independent system, all the pieces move differently (independently) which tweaks the house around and requires re-adjusting windows and doors on a regular basis. Slabs are better insulated and they are (generally) not damp and eliminate a whole host of problems. Yes, they are expensive, but based on my experience in the northern climate where the frost depth is 4-6 feet, it has been very successful. I have attached the slab drawing that I personally made up and had approved by the local city engineer where our park is located. If anyone decides to reference this drawing , please consult your local inspector first OR the manufacturer with whom your homes are made. It would be nice if the industry as a whole would just adopt a standard foundation/installation for all manufactured homes.MH Slab.pdf (151.5 KB)