I decided in the end to mount the USB and 12V connectors on the galley-driving compartment partition and to have solely the CPU fan in the bedroom. This makes connections a lot simpler though when I run my cables under the bus I might well add extras in case I change my mind later (a possibility).
Looking at my two Chinese connector panels, I removed 3 of the voltmeters and replaced two with Chinese USB connectors and one 12V connector. That should fit nicely on the aluminum box that'll soon be arriving.
My fuse array is set up for four fuses. Those will be fan 1, fan2, fan3 and sockets. The sockets need a 6.6v fuse for the USB, an unknown quantity for the voltage meter and something for the 12v socket. I only have two devices that run off a 12V socket and to be honest I do not know their amperage. One is a battery charger for AA batteries (it also runs off 120V) and the other is a 120v inverter that produces 200W. Neither of those, I actually use.
Thus, replacing the 12V cigarette lighter socket with another USB charger socket sounds much more practical. That'll have to be ordered but I think it'll work out far better value. That would take the total power from the USB cluster to 9.9A plus say 0.1A for the voltage meter or a 10A fuse. Combined with the fans totaling 3.5A, I'm now under the maximum limit of the charge controller.
As far as the other USB connector is concerned, I'll have to order it and wait - that's coming from China. Eventually I might use the dual connector I purchased the other day but not in the currrent iteration.
By the time I want a 12v cigarette lighter socket, I'll probably have upgraded my battery from 35AH and will probably have added extra power input. I did email somebody the other day that makes tiny gas engines for bicycles. They're quite inexpensive and at about 45cc would do well turning a car or motorbike alternation to develop power for a 12v battery independent of solar power. Solar is fine for a wide variety of things but the power produced while it will handle my small demands, won't handle much more. I certainly doubt all the online claims I've seen of being able to run air conditioning and fridges off solar.
Meanwhile, the subject of my mysterious battery drain came up at work and one old fellow that used to work as a bus mechanic then as a driver but who now works solely as an aide piped up saying that he would suspect the alternator. I tend to agree. Reading up on alternators online, it seems this kind of thing happens when the bridge rectifier built in begins to fail. There could be other reasons too but if I can get somebody to test the alternator then I might be closer to a solution. Otherwise I'll have to wait until I can get underneath the bus again.