Proclip.com has some multi-device mounts but they are pricy and I'm not sure if you will find what you need.
TakingThe5th - Chicago, Western Suburbs
'05 Ford F350 Crew 6.0 DRW Bulletproofed. Pullrite Super 5th 18K 2100 hitch.
'13 Keystone Cougar 333MKS, Maxxfan 7500, Progressive EMS-HW50C, Grey Water System.