It's been awhile but I've had many tanks plastic welded to install spigot, fill old holes, and etc. The vast majority were PE and many were way over 1,000 gallons. Simply never been a big deal. You just need to find the right house.
On the other hand, it's also easy to find places to custom make the tank just by taking in the old one and waiting a few days. Nothing about them should be expensive unless there are some oddball contours and etc.
Virtually all tanks are welded when assembled so poo-pooing welding as a generic statement doesn't fly. Granted there may be some issues with a tank where any repair is contr-indicated but finding a good plastic house would be my first stop.