Our foam was also too heavy for the struts. We did get a 10" extra firm though and the foam is more dense on the firmer mattresses. We use a rod to help prop it up. It's not so bad that the wife or kids can't lift it but I will probably try to upgrade the struts sometime.
Ours is about a year old and we still love it and don't notice any sagging yet, but that may be a difference in the firm verses plush mattresses. Ours also weighs quite a bit more than our original mattress. I needed help lifting ours.
Foam mattresses are shipped, vacuum sealed, in a box. Once the vacuum seal has been cut they are very difficult but not impossible to handle, with some help. I'm glad we had ours in the RV and on the platform before we opened it.