If you're asking my opinion, I believe all tubs that are not cast iron or have support that rests on the floor should be set in mortor or cement as a base. Even steel tubs will will give a bit if they don't have proper support. This goes for plastic shower bases as well. How many complaints have I got because the shower drain begain to leak because the shower floor gave when weight was added and sprung the seal right out of the drain lip.
As a aside I wish you would reconsider cutting back on the plumbing page. I know your a expert on dogs but,damm, you're good on plumbing.
Here's what the manager of the site had to say.
" Thank you for your help with the plumbing. It is the most popular category on the site"
I really need yeah here . Tom Ps. I saw the cartoon in this mornings paper. I have a permanent plumbers block.