How big is your budget
First thing you need to decide is will you normally be in a campsite (240v hookup) or not (need more batteries and solar)
Start with working out how you’ll use it, then think about what you want to be able to power (laptop, fridge, microwave, coffee machine etc) and then we’ll have a clue what to “guesstimate” for you
For reference, a cheap DIY solar (250W and 100AH battery) with say 6 24v or 12v outlets would likely set you back around a grand... for a “full suite” setup by a sparky with some serious gear (1000W+ solar and 400AH+ lithium batteries and a 240v hookup with a link to your tow rig for charging too) you could easily drop $5,000- $10,000?
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 100ah LifePo4 @24v +130ah AGM(2x12v), 40A Traceran controller, 780W solar; 1200w & 300W puresine inverters
120L grey/fresh water, 255L Samsung fridge, LPG Califont, 5KW Chinese Diesel Heater