So, I have nowhere near the expertise Bill possesses, nor the experience Bruce has. But, I did stay at a Holiday Inn Express last night.
If I understand you correctly, the primary use will be towing it to a location for a crowd of 20-100 people listening and dancing. Ease of mobility for storage is also a priority.
I like Bruce's recommendation for extension AND I like Bill's focus on sensitivity. For every 3dB increase in sensitivity, you'll get the same output with half the power... be able to run twice as long on a battery charge. (Not exactly, but loosey goosey talk, for the sake of conversation). I also agree that the sub enclosure you mentioned wouldn't be as effective as other options.
My recommendation is no better or worse than the others given. Just another option and opinion to ponder. If it were me, I'd build a full width T48 to put that 15" driver in (yes, the T/S specs are acceptable). I'd put it on the trailer lengthwise, yet firing to one side or the other, so the cab width is maximized in a vertical orientation without affecting the needed width of the trailer, keeping it minimized to as little as 24"/61cm wide (plus tires 'n stuff). Sonically, it won't make a difference which direction the mouth faces. I'd put casters on the end of the cab that faces rearward so the trailer could be tilted rearward until completely upright up on it's end, easily wheeled around tighter spaces, and take up a smaller footprint when stored. I'd put a top-hat in the top of the T48 and another in the side that faces up when in trailer mode so that you can pole mount your mid/high cab(s) with the trailer in either orientation and get the mid/high cab(s) above the crowd. Personally, I'd just build two 2x6" loaded SLA Pro's for tops. They're an easy build and they can be mounted one on top of the other and aimed the same direction for better throw when needed, splayed outward for wider coverage when needed, or aimed 180º for coverage in two directions. Or, you could even put them on standard speaker stands, left and right, for a more traditional "stage" type of venue/location.
I'd put your mono amp on the T48 and bridge the other amp for 2 channel output, one to each SLA Pro 2x6. I have used and like the Dayton Audio DSP-408
for signal processing. But, Mini DSP 2x4
is very popular too. I just haven't used it. I've seen some others pop up on the market from some of the car audio speaker/amplifier companies. But, in reading through their functionality and user interfaces, I don't think I'd appreciate them after using the Dayton unit. But again, I haven't used them so I really can't say for sure.
This plan would give you great extension, fantastic sensitivity, and excellent versatility. It wouldn't be as compact as the other options mentioned. But, sound wise, it would be the most impressive option, IMO. Especially capitalizing on, and maximizing the potential of the amplifiers on hand, too.
Whatever you choose to build, I highly recommend just building and using the passive crossovers in the plans (component values appropriately modified to accommodate your driver if need be). The parts are easy to source, they're easy to build, and ultimately will make it much simpler to get a sound you'll love. I get the allure to want to run everything on it's own amp channel. It's just not worth it in this case. But, feel free if it's what you really want to do.
If you have no idea what the Holiday Inn Express has to do with anything... Playlist: Holiday Inn Express commercials
Side note about the Dayton DSP-408: There's a Bluetooth option (not included) that gives tunability via smartphone (versus the standard method of PC via USB) and also allows Bluetooth music streaming... no other source needed. Could be handy.