The key is understanding that a "fiberglass" enclosure is fully dependent on a wooden structure.
From there [and a little basic understanding of structural concepts and the forces of physics at work on the enclosure from the simple force of the cone motion and the not quite as simple forces of the air dynamics inside the enclosure] it's more of an artform, in understanding how to cut your shapes and create your wooden structure in such a way that your fiberglass cloth will be stretched into the shape that you want when you staple it in place before applying resin.
All the basic enclosure construction rules still apply - with regard to the actual speaker location within the vehicle, the structural integrity of the enclosure itself and how that affects performance, etc.
Fortunately, a fiberglass panel that is only 1/4" is pretty much equivalent to a 3/4" piece of MDF or plywood in both rigidity and acoustics.
(I'd personally still recommend 'glassing in some ribs with scrap pieces of matting on the backside, wherever possible)
It's also important to note that resin cures with (and chemically creates) heat - and too much heat actually warps your cured product. So, there's some experience involved in knowing when your initial layup is thick enough to be warp resistant, and your ratio of hardener to epoxy is 'hot' enough to cure, but not too 'hot' to cause warpage.
There are some fun advanced techniques to learn too, that don't involve stretching a base cloth at all, that allow you more artistic flexibility - but even many experienced installers aren't aware of some of them, so my guess is the results you are looking for won't require those.
Select Products makes a brief video on basic fiberglassing that might benefit you - although it focuses more on using fiberglass to create enclosures like a spare tire well mold, where the outer surface is wood - which is a yet again different technique (involving a mold and mold release). If you are serious about doing more than this one-time enclosure, I'd suggest buying it.
The key is understanding that a "fiberglass" enclosure is fully dependent on a wooden structure. ;)
From there [and a little basic understanding of structural concepts and the forces of physics at work on the enclosure from the simple force of the cone motion and the not quite as simple forces of the air dynamics inside the enclosure] it's more of an artform, in understanding how to cut your shapes and create your wooden structure in such a way that your fiberglass cloth will be stretched into the shape that you want when you staple it in place before applying resin.
All the basic enclosure construction rules still apply - with regard to the actual speaker location within the vehicle, the structural integrity of the enclosure itself and how that affects performance, etc.
Fortunately, a fiberglass panel that is only 1/4" is pretty much equivalent to a 3/4" piece of MDF or plywood in both rigidity and acoustics.
(I'd personally still recommend 'glassing in some ribs with scrap pieces of matting on the backside, wherever possible)
It's also important to note that resin cures with (and chemically creates) heat - and too much heat actually warps your cured product. So, there's some experience involved in knowing when your initial layup is thick enough to be warp resistant, and your ratio of hardener to epoxy is 'hot' enough to cure, but not too 'hot' to cause warpage. ;)
There are some fun advanced techniques to learn too, that don't involve stretching a base cloth at all, that allow you more artistic flexibility - but even many experienced installers aren't aware of some of them, so my guess is the results you are looking for won't require those.
Select Products makes a brief video on basic fiberglassing that might benefit you - although it focuses more on using fiberglass to create enclosures like a spare tire well mold, where the outer surface is wood - which is a yet again different technique (involving a mold and mold release). If you are serious about doing more than this one-time enclosure, I'd suggest buying it.