I just had the same thing happen to me today. Good brake check before we hit the road this morning, so I know the timing.
Big Rig driver pulled up beside us on I-70 west of St Louis and told us we had no brake lights. Pulled over immediately. Front signals worked, TOAD signals worked, reverse lamps worked - but no brake or turn signal.
Checked fuses and then got on the blower with Coach-net. They couldn't help. Crawled the length of the MH looking for a broken/disconnected harness and didn't find anything.
Finally Googled the problem and found a similar thread from last year. All four lights died at the same time. One cracked and the other three blue/black.
I suspect that the culprit was a VERY HARD hit on the rear suspension to a pothole right as SWMBO hit the brakes. Heat, mechanical vibration and age finally did the cheap no-name China lamps in.
Would have never thought to check bulbs when all four were out. Backups worked. Thank goodness for this forum!
BTW - mine were bone dry and no signs of corrosion. Just crappy bulbs and a lot of vibration.
Will be looking at alternatives. There are a lot of 1157/2057 LED options of Am@zon but I've read tonight that they don't really do the trick. Bargman makes a retro-fit kit for the lights on the back of the Sunseeker but they are about $30-35 a lens. Or you can replace the whole unit (Brake, Turn, Tail, Back) for about $50.
$100 seems like a lot for new tail lights but the flip side is getting rear-ended after loosing all of your tail lights (without knowing it) would cost a lot more. Might give the $5 1157 SMD LED clusters a shot first and see how they look compared to a regular incandescent.
Good luck to all - my recommendation if you have a new Forest River is head to the nearest car parts store and pick up 4 spare bulbs. $5 is cheap peace of mind.