Well, if "Cheaper is better" then there are a few places you can save money and a few places you can save space, but it's really, REALLY hard to do both.
A pre-built will save you the most space but you'll lose out on capacity over a complete DIY setup. DIY battery is usually 30% or more cheaper than a pre-built LFP battery and you can get MUCH higher capacities in the same physical space.
As Eggo mentions, grab the Power Audit form and run through it a few times. The first pass throw everything you could ever want in there. Aircon, jacuzzi, MargaritaMaster-9000, whatever. The second pass will be the "I absolutely NEED this to live" which is going to be restrictive but cheaper. The 3rd pass you can be more reasonable to your wants and needs and now that you've had a little practice it'll come together nicely.
You're probably looking at a
simple 12v system so you don't have to deal with buck converters and the like. Keeping a 12v system for your 12v devices keeps things simple. For your needs it sounds like a 1200w inverter would be more than plenty so don't panic about that.
As for solar panels, you're going to take a performance hit if you lay them flat but it's MUCH easier when you're out & about to not have to pack 20lb panels out and get them set up. Used panels online are averaging about 250-ish watts for $100 so grab your measuring tape and figure out how many panels you can physically fit up there. Yes, there are lighter flexible panels but as a general rule they suck and are overpriced for the convenience of the lighter weight. Remember that your budget has to include things like breakers and wire and racking.
Plan out where you're going to stick stuff too. A dozen 3000Ah batteries sounds great until you have no passenger seat anymore and you're dragging your axle everywhere. The biggest advantage that pre-builts have is that they can stick all the parts needed (battery, SCC, inverter, etc) into a physically smaller space. You can also roll something in between like a
Licetti Power Box unit which seems to be about the best of both worlds. You'll still want an exterior SCC for your panels as the one built in is only 10a which is pretty useless. I have a 40a SCC I rigged up for mine that just plugs into one of the Anderson ports on the side so I can get more panel involved. I even
managed to get 300Ah of battery inside there so it lasts all week long on the camping trips.
Rough budget numbers assuming going the cheapest & simplest route:
Licetti AC Power Box - $200
4x 304Ah LFP cells - $600
100A 4s 12v BMS - $70
Cheap-ass 40a MPPT controller - $100
2x 250w used solar panels - $200
12v fuse block, Anderson connectors, fuses, 14g wire, hammer crimper, lugs, etc - $150
12v 5Kw diesel heater - $100 (I know WWAAYY too much about those if you need tips)
You'll probably hit about $1300 or so for the complete solar end system, maybe less if you look around for sales and the like.
And post pictures, we LOVE that stuff on here! ?
