I run my fridge on propane when on the road all the time. What states is this illegal in? Dometic, my fridge manufacturer, even makes a wind kit which facilitates this, preventing the flame from going out when buffeted by big trucks passing and side winds while traveling down the road. Of course turning off the propane while fueling and traveling through tunnels both fulfills the laws to this effect and makes good sense.
For solar powered boondocking, a good compromise between a $3,000 Sunfrost fridge and $500 residential fridge is a Novacool DC fridge. It has a high-efficiency Danfoss rotary compressor (like mini-split heat pumps use) which runs off of 12 volts, so no inverter is used. Its efficiency is about half way in-between a Sunfrost and a residential fridge, mainly because of less insulation (extra insulation can be added upon install to boost its efficiency) and so is its price ($1,716 for a 9cf model.) "Adding 2" rigid foam insulation to the outside will reduce energy consumption by 1/2. 1100 watt hours per day at 70 degrees as delivered, 550 watt hours per day if insulation is added on-site."
http://www.backwoodssolar.com/novakool-dc-refrigerator-model-rfu9000
Even at 1,100 watt/hrs./day, about 250-300 watts of solar will replace what it draws. Add the extra insulation and only 1/2 of this solar capacity is needed. For comparison, 2 typical golf cart batteries have about 1,200-1,300 usable watt hrs. (if depleted to 50%) So 4 golf cart batteries would be good for about 4 1/2 days of use between charging if no solar is present and nothing else is used (with the added insulation and a little over 2 days without it).
If you're looking for a reasonably priced, energy efficient residential fridge, (and don't need or have space for a giant one) the best I could find is the 10CF Frigidare FFET1022QW. It's only $432 from Sears and according to its energy star rating only consumes 296 KWH/yr.
http://www.sears.com/frigidaire-10-...4602442000P?prdNo=42&blockNo=42&blockType=G42
Of course you still have inverter inefficiencies to deal with. This equates to 811 watt/hrs. per day. Assuming a 50% duty cycle, (which is typical) This means it draws about 67.6 watts, which is only .563 amps at 120 volt or 6.6 amps at 12v (with the same 85% inverter efficiency). A 200w dedicated solar panel should do it, as long as you have enough battery power to last for several overcast/rainy days. Four GC-2 golf cart batteries should do the trick. If you choose to buy the $1,716 fridge (and added extra insulation) you would only need about 135 watts of dedicated solar. However, the extra solar panel and battery capacity cost say $3/watt, or $195 would be much less than the extra $1,284 the high efficiency 12v fridge will cost, saving you $1,089 if you have the roof space and added weight capacity on your rig and assuming you already have an inverter with sufficient extra capacity.
Chip