Your hot water heater is a standard unit used in many, many RV's. You can purchase replacements at most RV dealers, and, if you have the model number, there are also a number of good internet sources.
The plumbing in the '99's is standard PEX fittings for the most part, readily available at hardware and home improvement stores.
If the microwave does not have power, first check to see if it is plugged in. In my '99 the plug is in a socket in the next compartment, but yours may be slightly different. Then, check the circuit breaker. It may be off or tripped and need to be reset.
The radio is on the 12 vdc side of the system. There is a separate fuse for it in the fuse panel but there are also fuses in the wiring harness right behind the radio. You'll want to check both. Also, there may be one or more wire nuts in the radio wiring harness behind the radio. It's possible one of them is loose or missing.
If the other 12 vdc items like the lights are working, that should narrow things down pretty quickly.
FWIW, the radio in my '99 crapped out long ago. The lighted panel stopped working so I could not see what station it was tuned to. My solution was to install a standard car radio. I got one free out of a "cash for clunkers" car, but if you are an automotive tech, you've likely got sources too. Worst case (money wise) but easiest install and retro-fit is an aftermarket unit.
See this thread for my details on the swap-out: http://www.sunlineclub.com/forums/f6...ighlight=radio
'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
Amateur Radio kd2iat monitoring 146.52