a mobile home is a trailer, usually on wheels w/ lattice work or such to hide the wheels to make it look, not so much like a trailer. shouldn't build a tank like that in one. why would you build this to have it not be permanent. if it is actually a manufactured home on foundation, it'd be o.k. just make sure it's a thick foundation.
You would be better off converting a shipping container. They are iron and can be picked up easily by a large forklift or crane. Come in 20 foot or 40 foot sizes and usually quite cheap for a second hand one. U just need to cut out some viewing windows, attach some glass or acrylic panels, waterproof the interior and voila.
I worked at a yard that delt with them and you can get a run down one(40') for about 3g's and the 20' long one for a bit let then that... well considering that they are 20g's new thats not bad. but... umm, thats neither here nor there...
I went fishing offshore out of Daytona last week. We lost count of the sharks we caught. Let me know when you are ready for some real sharks and I'll donate some to the cause
Ummmm I have actually done this with a shipping container and it is quite cost effective if you are a handy DIY. I have also used old shipping containers as temporary fishrooms too. But the cheapest and still portable large tank would be an above ground pool with some viewing panels. I have made 10,000L tanks for about AUD$350 with viewing panel installed.
Before someone asks, No I dont have any photos with me as I am overseas for a few months. I do have some other photos of some other commercial large tanks I have installed....