If this is the case, then I highly recommend you make that, and make sure it’s strong enough to bash around and flex, before you begin purchasing the other components, aside from a deck and helmet. Jump on the deck. Make sure the bolt holes don’t crack. Because they will probably crack. People use fiberglass a lot for reasons. Glass fiber also doesn’t block radio like carbon fiber does and it’s a good bit more flexible.
However, this is a better option if you don’t buy an enclosure (which limits deck choice)
Last thing you want is to have a battery and try to find an enclosure that works. (Unless you lay up your own fiberglass enclosure) Do that the other way around. Tell the battery builder how big your space is.
Of course you can make the enclosure with certain common battery sizes in mind, I just wouldn’t buy that battery yet