Bill, if you have a TITANIUM 5-er, you probably also have a diesel truck with 2 batteries. I tied all three, same size batteries together in parallel (with a low number cable) so the truck’s alternator charges all three and the 4545 Wizard charge center does the same with the help of our 200W of solar when the engine is off. For 20 years i’ve been told we are living on the edge with this, but so far, so good. Only once when I foolishly left the fridge on 12v for 5 hours overnight did it take down all 3 batteries. All three batts were marginal by this time with 6 years into them. The only woe I’ve run into is parking the TC in its shed and not having any sun to keep the batteries charged over months and months of non use. The shed has no power. When the sun comes out, which has been very rare on the west slope northern Sierra Nevada this winter, the TC is basking in the sunlight with green lights abounding.
The only other option I see for you, since I have the same footprint TC and battery box size as you, is to measure the battery box and find a couple of smaller 6 volt golf cart batteries to see if they will fit. I have not tried this. For the first 15 years with the camper we used 12v to run the fridge while travelling since the flame kept blowing out using propane on the road. My RV guru showed me how to shield the flame so we now turn the propane fridge on at the beginning of a trip and just leave it on for the duration. It’s much more efficient anyway. We rarely use hookups. With no oven, no microwave, no air conditioner, we were very cognizant of power usage and have never had a problem since.
2020 Ford F-350 XLT FX4 4WD SRW SB SC 7.3L Godzilla Gas TorqShift 10R140 397 amps dual Alt dual batts Frnt Dana 60; Rr Dana M275 E-locker 4.30's 4580/4320/4066# payload 7243# curb wt. 11,300# GVWR 5-er prepped. 2020 Northstar Laredo SC, 12v compressor fridge, cassette, 320w Solar sub zero insulation.