I'm not convinced this is the right boat.
Firstly towing your RIB to a venue, having two Oppies to rig / supervise the kids rigging, children to make sure get changed, registered, briefed etc do you really want to be assembling a SIB and putting an engine on etc. If it was a RIB on a trailer - you may find another club member / volunteer will offer to launch you while you do the necessary with the kids. They aren't likely to do so with a boat that needs built!
You will need 2 MEN lift for boat etc.
Secondly, on the water is it the right craft. You will spend a lot of time stationary. Perhaps others can comment but does it drift more than a RIB? More importantly though, is it the craft for righting a capsized dinghy from or for towing from? Yes you will be OK towing one it, thats quite easy in pretty much anything. But at an Oppie event you will usually be on a 1:8 ratio. If you want to be in the RIB numbers you need to be able to tow 8 oppies daisy chained in anything up to F6. Thats a big ask for a 25HP engine on a fully inflatable base. Perhaps others will tell me I'm wrong. If you aren't planning to be in the 1:8 numbers, expect even less help rigging and a good chance some venues wont let you launch.
Thirdly, you will want to carry some kit. Anchor, chain etc so that if you have a problem you can stop. You'll need 2 crew. Plus possibly snacks for kids, first aid kit etc. None of which has a home on a SIB. You need to be able to take a mast off an Oppy and put it in the RIB on the floor. (Towing oppies with sails flogging for long distances upsets darling oppy parents who just spent £550 on a new sail to add 0.01knots to their cherub's speed) - thats about 2.5m Will you have space to actually put that in a 3.8m boat?
Forthly - launching - No trolley - so launch wheels? I like launch wheels. I hate things sticking u on my RIBs when there are tow ropes, mainsheets etc involved. They just get tangled.
Fifth - If your Oppies end up on dodgy bits of beach - is a soft bottom the best thing? Certainly my club won a 4m+ Honwave in the Honda RIBs a few years back and paid to upgrade to a Highfield because they couldn't see the Honwave lasting.
So your problem is how to get a RIB there and back plus two oppies. You can put one on the car roof. leaving just one to worry about if need be. But you can fairly easily get a trailer modified to add a carrier. Heavier example than you need here:
https://cache.apolloduck.com/image_b...jpg?1493144660