I agree, as long as you do not spill water all over it, you should be able to get away with just two coats of primer. Make sure you do "2" coats though since MDF sucks in the primer.
Although keep in mind that if you have a party which includes a keg of beer and someone (who might be on their 8th beer ... since it is free

) spills a bit, you do not want it to leak through any crevaces (sp?) and get inside.
What I personally did was two coats of prime on everything outside of the cab and also everything inside the cab which was around cracks and spaces. I also painted my cabinet black and painted the places I primed inside my cab black as well so I would not see "white" color through any holes, gaps, etc... from the outside.
Ok, rambling....I will stop...good luck.
PS: God for bid anyone sets their beer "on" your control panel !!!!!!