Yea - it is awfully close to that metal lid. I'll be thinking this through as I'll eventually want to replace the group 27s with GC2s.
o Replace step with wood or fiberglass
o Add an insulating layer to the underside of the step
o Raise the step & hinge by 1/2 inch or so perhaps with a spacer made from a cutting board
o Shorten the studs on the GC2s
o Remove the studs on the GC2s, use another attachment method with the posts
o Cut the bottom out of the compartment & add a new bottom 1/2 inch lower
o Abandon the idea & stick with Group 27s.
Here's some size and amp/hr charts for common battery sizes:
List of Common Battery Case Sizes | BCI Group Numbers
DIMENSIONS IN INCHES: 12.00" 6.63" 9.06" LxWxH
Amp Hours (AH): 90
DIMENSIONS IN INCHES: 10.38" 7.13" 10.88" LxWxH
Amp Hours (AH): 225
They have the GC2 listed at 10.88; which is a tad taller than my measurement of 10.5. I wonder if other brands are a bit taller. I measured the Costco GC2s in my old motorhome.
Yea, it'll be a interesting project...