For anyone else looking, I went with a Torklift Lock and Load Model A7752 (they also make a smaller one for smaller Honda eu2200i and comparable models) + a pin lock: https://www.torklift.com/rv/lock-and-load
I almost went with a KSH Marine box that you can take the sides off when running the generator but it didn't have a mount. My RV shop said they could weld it but then I couldn't open the back door AND after thinking about it I may be using the generator on two different vehicles and it would be nice to be able to take it off if needed for super tight parking spaces in a city. KSH quoted $398+shipping & handling (additional $150 for powder coating) for the Honda
Handi eu3000i (Quotes are only valid for 14 days). The link is here: https://kshmarine.com/photo-generator-boxes/
Their phone is Monday-Thursday, 8:00-4:00 at (92
680-6610. Super nice people and a very cool product.
For more Sprinter type applications I found this which is amazing but just not in my price range or for my needs: https://www.aluminess.com/accessories/boxes/
Super cool though!!!!
For people with a smaller generator such as the Honda eu2200i you might like these:
This one also makes one for the Honda eu3000is but not the Handi 3000i:
LowPro LockDown. Keep what’s yours.
There are more for the 2200 but I lost track since I don't have that model. Anyhow - hope it helps someone else save some time!