You've not mentioned where it is that you will be using your fridge. Could you use a cool box?
I spent a deal of time looking and decided I didn't need a powered or gas fridge as im simply not likely to ever be routinely far enough away from civilisation to justify it, and the extra convenience wasn't justified by the extra money.
As has been mentioned, if you're routinely doing a week at a time with no contact in oman or morocco then a fridge makes perfect sense. But for cutting around the Uk, I opted for a good quality rotomoulded cool box. If however, you are already adding a split charge/leisure battery for other reasons, then the cost is rather different.
Advantages:
-Even the most expensive cool box is FAR cheaper than an electric fridge when you include costs of split charging systems, dual batteries etc.
- Doesn't require carrying any gas, which is a boon for travelling the continent where transport of dangerous goods could even see a propane cyl scrutinised
-Very easily demountable, just chuck it in the back and lift it out when you need it. doubles as a handy seat too!
-reliability, you'll never lose a compressor or fry the PCB
-more storage volume for the size as youre not carrying a compressor too.
Disadvantages:
-You can't freeze stuff, or keep it frozen*
-requires planning, as you will always need to pre-chill it for the best performance
-Requires maintenance, you'll need to top it off with ice as and when you can in use.
-putting warm beers in your cooler will negatively impact it's performance.
-Approx 2/3 of your space should be taken up by ice. which rather negates any extra storage you would have had from not carrying a compressor. However, cleverly freezing drinking water bottles, OJ and milk can certainly help minimise this.
-You will want to minimise opening and closing of the cool box, some may find this very inconvenient. Especially if you have kiddies who like to pull cokes out of the fridge every 20 minutes.
*You CAN keep stuff frozen pretty well depending on how well you pack the cooler, and you CAN freeze stuff if you use dry ice to supplement.
There are some good videos out there about how to use and pack a cool box effectively, and I reckon I could easily keep enough food frozen in my box to last 2 people a week. Using dry ice is another option if you get a good box (YETI explicitly say you can use it, other manufacturers may not). Though for some purposes it can be too cold, and cause beers to freeze and explode!
I got a YETI Tundra 65 and it fits my defender loadspace perfectly when placed width ways. The 75 would probably be slightly too big, and too heavy for 1 person to manhandle.