Safarifriends.org

The last time I shopped for an air filter Rock Auto had the best price - $146. It's out of stock now just like everywhere else but there's a good chance they will have the best price when they have more. You can't find it by application but if you search 'WIX 46857' it will come up. They have it err...

The mileage and hours sound about right. I won't be changing mine every 6 months though.
When you're talking about 7+ gallons of oil for a change getting oil analysis is a cost effective strategy.
Have your oil analyzed at 8K-10K and make the decision to change based on the results.

It looks like the previous owner had 6 12-volt marine batteries in there. Can you do that? I know the 6 volt batteries are about 1400 for 6 of them. You can have as many or as few 12V batteries as you want. They are connected differently - all wired in parallel. https://power.sil.org/wp-content/upl...

Six 6-volt batteries wired in series-parallel for a 12-volt system.

On my 97 Ivory the drain valve is access from the front basement compartment. It's on a pipe that's against one of the basement support hangers. If you look underneath the coach you should see a pipe that's open on the bottom sticking straight down. Your valve should be directly above that.

The "Safari Motorhome Owners Group" on Facebook has a pretty good file library. You'll have to join the group to gain access.
https://www.facebook.com/groups/165304860342760

The sleeve could be something as simple as a piece of 3/8" or 1/2" pipe cut with a hack saw.

Doesn't have to be allthread. A grade 8 bolt of appropriate length will be stronger. Add a length of pipe or tube.

The problem with towing without disconnecting the driveshaft is the transmission relies on an internal pump to lube the moving parts. Even in neutral internal parts spin and they need lubrication or something will fail. Removing the driveshaft would not affect the lights on the control panel.

I've never seen any 'whole coach' wiring diagrams. Instead diagrams are published for each separate system. Transmission diagram from Allison. Engine diagram from Caterpillar, etc. I'm attaching a couple of files that may be helpful. Also, take a look at the file collection over at the Facebook Safa...