I'm not sure about the dimensional differences of the compartment itself (280 vs. 345) but I'm pretty sure that access to the compartment is better on the 345. If yours is like mine then you basically have a big access door on the drivers side. The door opening is 36" x 18". The GenSet on mine is 33.5" x 19" with the carb and air cleaner bolted on and 17" with it removed (measured to top of the control box).
The GenSet is bolted to a metal pan which is attached to the floor of the genset compartment with four bolts. Once disconnected it should come straight out the door? Lifting the weight of the GenSet while it's still in the "hole" is your biggest problem.
87MH has removed the Onan from his 345. I think he had to use a forklift to lift it out. Perhaps you might send him a PM for some information from someone who has "been there done that" on a 345.
You might call around to your local RV Dealerships for a book rate on an R&R for a GenSet. It might be a little different for you if you switch to Honda in that the 12V
, 115V and fuel connection locations may change or require modification to work with the Honda.
As far as getting a new Honda in there; I found this on the NorthernTool website for the Honda 6000 Watt RV GenSet:
Dimensions: 25.59in.L X 19.09in.W X 14.17in.H
REQUIRED COMPARTMENTAL DIMENSIONS: 28.11in.L X 21.49in.W X 15.23in.H
AC OUTPUT IS 120V: 6,000W (50A) CONTINUOUS & SURGE
Fuel Type: Gasoline
Looks like it's considerably smaller than the Onan....so it should "slip right in" - right?????
Please continue to post your findings on this thread. We're all facing Generator replacement at some point and I for one have considered the Honda as the logical choice for me when the time comes.