Another vote for Newmar. We bought our new 10 years ago and had approximately 100 custom changes done to suit us and our full-timing lifestyle. At that time they pretty much would do anything you wanted except for any changes that would affect structural issues.
Again, as full-timers, we didn't care where we bought it because we knew we probably weren't going to go back to the dealer unless we were in the neighborhood. We worked with Newmar direct in Indiana with the changes we wanted. Then we emailed our specs to approx. 20 dealers throughout the country. They were all bidding on the exact same unit so the one that came back cheapest got our money.
When we received it and drove it a few months, we had a few very minor issues we wanted corrected. The Newmar mfg. in Indiana set us up with dealer where we were traveling, sent any parts needed and when we arrived everything was done in a day. We had no further issues that required a dealer.
We have a Spartan/Cummins/Allison and no problems with Spartan and we've gone to Cummins for basic maintenance and check overs. They're all over the country.
We travel constantly and even took a summer for driving to Alaska with absolutely no problems to our Newmar. It rides beautifully and smooth and everything has worked just fine.
We would definitely advise that you get a side radiator. You won't be sorry.
Perhaps you hear more about Tiffin because there have been some very major problems with some issues with Tiffin and yes, good ole' Bob, gets you in for repairs. However, those issues should not have been built in the first place and they kept doing it. I'm not saying that Newmar is 100% and with every new unit of any manufacturer of motor homes there will be some issues but they usually all pop up during the first year and once corrected, that's it. With Tiffin, folks seem to go back to Red Bay constantly for the same repairs. We have friends who have done that and have spent weeks at their facility waiting for the repairs to be done. You just don't hear that about Newmar. We chose Newmar after talking to many, many Newmar folks in campgrounds. We didn't hear of one complaint and we don't have one either.
Good luck with your choice.