Take a look at k9sprinter's rig here:
viewtopic.php?t=5616
I was always impressed by how much he was able to pack into his layout including crates for 6 big dogs.
As far as who to talk to at Sportsmobile, I don't know who is there currently, but in 2010 I worked with Jonathan Feld. He is Alan Feld's son and I think these days he may have sales reps other than himself who take care of working with the customers. They were very accommodating when I came up for a tour and a test drive. Just be sure to make an appointment well in advance. Let them know that you have some custom designs and would like to speak to someone who can advise you and they should be able to answer any questions. They are a busy shop but I have always found them to be very friendly and hospitable.
If you end up going forward with a custom build, ask for plenty of photos to be sent to you during the process and plan to make a few trips up to Fresno to check on things in person at key points. Mine is an EB-50 with a few modifications and one of my special requests was forgotten, but since I caught it during the build, they were able to correct things in time.
Steve in L.A.