It's real easy.
I'd start with running US Battery 12VRX XC2. It's a 150AH 12v golf cart battery, with this battery at a 25amp draw youve got 292 minutes of juice. If you wanna go crazy US 185HC XC2 (220AH) with this one you've got 443 minutes at 25 amp. They batteries are cheap $192 for the 220AH and $160 for the $150AH. The 220 would supply you enough juice to probably small stuff on it for a weekend without recharge.
If you ran a 1500watt heater they draw 12.5 amps, make a guess that a small one might draw 5 amps. I'd guess you could run over a weekend and charge when you get back home.
BUT.
Renogy 100 Watt 12 Volt Monocrystalline Solar Panel (Slim Design)
Rover Li 40 Amp MPPT Solar Charge Controller
You'll need cables to mount.
Heres where the big expense will come in. That heater if a regular home one will need A/C. So you'll need an inverter and not a cheap one to feed it. If you get a DC car type ceramic heater you can wire directly off battery.
SOLAR PANEL - TO - MPPT CONTROLLER - TO - BATTERY.
ACCESSORIES THAT ARE DC CAN RUN STRAIGHT OFF BATTERY OR DISTRO PANEL.
The MPPT Controller will also have a fault protected power output you can run the heater off if DC.
You have to spend $3000 on a Goal Zero to get $280ah in a small portable unit. If you ran that single 220AH battery a 100 watt panel and the controller you'd be in about $550-650 and have the same power, recharged by the sun all day everyday, the downside is it's not portable.