I installed FreeFit, and the guy at the store suggested using a latex primer or RedGuard to seal the floor in wet areas, in case something got underneath the planks. 

@Paul Ewing Very good point about the durability of prefab pans.The right solution is use deck mud underneath the pan to fill the air space so there will be no flexing.  

Will they cause a cavity as they decompose, or will their decomposition just create soil or something?

Problem is if they remove it and find it was leaking, or any contamination in the soil nearby, then it can be very expensive to remediate, and at that point, you have spent the money and probably won't close, so you're out of pocket and did the seller a favor, which sucks.

Possible hidden damage in this area.Recommendation: Chemically treat the soil at probable entry points for the control of subterranean termites.Remove any termite shelter tubes from accessible area.

They are trying to get a fire lit underneath you.Your original post was very detailed and you included how you felt bad about the kids/family/whatever.

Everything is roses until they stop working and the soil doesn't perc anymore or you run out of room for a new field.

I installed a cheap fiberglass tub 5 years ago without mortar underneath it (my fault) and my tenant cracked it in November.

Clay soil, tons of predators, heat waves that fry the veggies on the vine, and Fire Season - thin skinned flesh picks up the flavor, and it is Not a pleasant one....but, it's so rewarding watching something survive all that because you helped!

Hello,I have put down an offer on a duplex in the Bay Area and did an inspection on the foundation and found that the floor was sloping due to the soil in the area.