They really aren't difficult to pull out. Our shop has a nice cradle and strap system that works well even for diesel gensets up to 12.5kw. You could easily create your own much quicker/cheaper than designing/building a slide rail system. Harbor freight transmission jacks work great and are very inexpensive. Most gensets have 4-6 bolts holding them in from the side and the 120VAC wiring, fuel line and remote wiring disassembles in a matter of minutes - and its out.
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified