I'm planning on purchasing the above custom box. I emailed the seller regarding the volume of the box and was informed it was 1.0 cubic ft.
They sell the box with 2x 10 subwoofers from JL audio, which required volume is 0.625 cubic ft, I assume that's only for one? Correct me if I'm wrong.
But I look on purchasing the subwoofers separately, looking to get CompVR's from Kicker which minimum requirement is 0.8 cubic ft. Am I safe to assume my subs won't pop?

what kind of mounting depth does that even have? it looks like the right side barely has any backspace.

the box itself looks flimsy as hell on top of that. even moreso if there isn't a center divider in it.

you'll also need to keep in mind that once you add the sub itself it removes even more air space so if you are only getting .5 cubic feet of air space per sub before displacement you are going to have to be as close to .5 minimum requirement as possible to even have a chance of them working correctly.

how much as the asking for the box?
how much for the 2 subs?

building a small enclosure isn't hard. if you have power tools and ever built anything with wood you can make your own with MDF in a few hours.

IMO, that looks like a junky box.
Build your own/have a friend build one for you. You could get a much more secure box with perfect dimensions that way.