Dan, paralleling fuses is not a particularly good thing to do. Yes two paralleled 30 amp fuses will carry more than one 30 amp fuse, but it is anyone's guess how much more. The reason being is very small differences in the installation resistance of each fuse will determine how they heat and hence how the blow.
As others have said, if the fuse/fuse holder is getting hot; something is undersized or the connection to the fuse and/or fuse holder has developed some resistance. It is a know fact that maxi fuse holders (those big car type fuses) will develop contact resistance when driven hard for a while. I think NeilP who posted on here had some bad luck about a year ago with some and posted pix, I think.
A fuse's voltage rating is the supply voltage that the fuse is guaranteed to break. Note that AC goes through zero current each half cycle, so it tends to want to extinguish the arc on it's own. DC is a beast. With the inductive kickback of the leads and no zero crossing, DC fuses at high voltage and high currents are a big plasma ball. You will note that fuses in this category are typically big, expensive and have some type of ceramic in their make up.
The trouble is eBikes a pushing the 100 volt limit. Lots of nice Forklift fuses below that, but the territory gets less populated and prices higher above 100V. Will a lower voltage rated fuse work at higher voltage? Likely, but not guaranteed. Will it blow, yes; the question is will it extinguish the arc. If you can ramp the current down to zero, like letting off the throttle, it certainly will.
A fuse worth looking into is the "Pacific Fuse" at autoparts stores. It is rated to 58 volts I think, and some come with tabs that you can bolt to or solder to. I would load their catalog, but it is 8 Megs. It has the time/current curves in it so that you can see how a fuse works. They are not instantaneous, and they are not perfect. They do save the wiring harness. That is about all they are good for as the silicon typically blows anyway.
Good luck with your bike and your fusing.
PS: I bought some nice looking 100 amp CNL fuses from China. Thought I got a good deal on them, but after an experience another member on the board had with some, I tested one to make sure it blew. It did ... at about 350 amps! A lot of good that would do. Counterfeit fuses are about as useful as counterfeit drugs.
