one remote turn on, 2 amps?

Try the daisy chain method switch hitter told you about, it's easy and there's no soldering involved.  If you need to put in a relay to provide enough voltage to each amp, you can pick up a SPDT at RadioShack or other places.  Here's how to connect:  https://www.the12volt.com/relays/page5.asp#rtol  (...the second amp turn on is the additional device...)

The sum of the fuses you should use will be a small number, as each amp will need just a 1 or 2 amp fuse in the turn-on wire.  The fuse you should put in the 12V constant power lead should be at least equal to those two fuses.  Radio Shack will have the small fuse holders and fuses, too.

You could even use a 1/2 amp fuse on a remote wire.  I used one (this one) on a remote turn on wire that spits to two amps and it's been fine for a year and a half so far.  Here's a fuse holder for that fuse.