I've re-purposed many old Peavey cabs. I took two old PA cabinets (ported, 12" speaker and a piezo), put a couple of MCM 350 watt 12" speakers, cut a hole where the piezo was and put in a sealed 6 1/2" midrange and 800Hz crossover, and I've got a couple great bass cabinets. They are about the size of those Ampeg SVT-210AV cabinets. They had WAY too much low end, so I sealed the ports, and they sound great. Stacked, they have a small footprint, and I can hear as one midrange is near my ear.
My old main cabinet was an old PV 115 PA cabinet. I put a 4 ohm Kappa pro, and put two 4 1/2" Bose speakers where the horn was (angled in, in their own enclosure) and crossed over at 800Hz, and that cabinet kicks...and it's small.
I just got a strange PV115...shallow, slot ported, with an original 150 watt Black Widow and two piezos. I was going to put a 4 ohm Neo in it, but it actually sounds great. I did stuff insulation in. I got it cheap, and it's small, light and will work great for our band.
I'd close up the back in that 115e, and a better speaker, stuff it with insulation and give it a go. MCM Electronics has inexpensive speakers that have worked great for me. I have a 500 watt 15 in a small, sealed cabinet (the size of the rack mountable Peavey's that were around in the 80's.) It doesn't have enough high end to be used alone for bass, but it has made one excellent sub. I have two of those cabinets, and it smokes the EVM 15L that is in the other one.
Check this page out. If you get the sales flyers, (they can be accessed on their site) the prices are usually even lower. That 200 watt 15" also comes in a 4 ohm, which would help your amp produce more power. Many of their speakers do.
