40 amp fuses are available in the standard size, but it is hard (impossible?) to find fuse blocks for th standard blade fuses that are rated at more than 30 amps per position or 100 amps overall.
I use these fuse blocks with 40 amp fuses in two positions (of the 8 available) for the batteries. I've got a 45 amp converter (Intellipower 9200 series) that has its own dual fuses, so I connect the inverter directly to the buss bolt.
ATC®/ATO® Fuse Panel w/o Grounding Pad
I don't use any high power inverters, so there's no normal sitution where I'll have a need for more than 25 amps or so at any time. If something goes haywire and the amps jump up, the overwhelming probability is that they'll jump way past 40 amps and fuses will blow right away--I'm not concerned that the fuse block will exceed it's short-term amp capability.