I would assume that those are external dinemsions.

We can assume it is likely built from 5/8ths material, or 3/4 material. At the dimensions provided, and assuming a perfect rectangular enclosure, that gives us a gross interior volume of somewhere between .59 and .61 cubic feet.

Then, as you notice the baffle and the two sides, (vinyl covered) are inset, and it sort of appears that there is an angle to the enclosure; i.e. the top is shallower than the bottom. The scalloping in the inside back of the enclosure further points to the probability that this is an engled box. Both these points tell me that the enclosure might be as small as .5 cubic feet, maybe smaller. In my opinion, that is really too small for what you are looking to do.

Another thing to point out. The scalloping on the inside back of the enclosure is there to provide extra mounting depth. If your subwoofer is deeper than the enclosure is, it will not fit.

One more thing. 10-inch woofers are the worst of the group, (amongst 8's, 10's, 12's, and 15's) at having a very wide range of cutout dialeters. A 10" woofer can have a cutout diameter as small as 8-3/4 up to 9-1/8th as I recall from my history as a design engineer designing enclosures for other major brands. The enclosure you are looking at is probably a compromise in terms of its hole cutout. Make absolutely sure you center the woofer perfectly in the hole, or you will find some screws do not bite and/or you end up with leaks.

You are only talking 20 bucks, so it is a cheap experiment, but $20.00 would go a long way towards buying material to build something that is exactly right for your woofer.

If you can, take the time to find out if your woofer will fit prior to handing over the money.