Maybe a couple different issues here.

1- Don't add stuff to existing circuits.  The ones that are there are designed and properly fused to take the loads that are designed into the truck (some only margially so).  If you need to add circuits, install a secondary fuse panel.  The ones you can buy from the auto parts stores are cheap, reliable, and use the blade type fuses that are a lot more reliable than the bullet fuses the factory uses.  If you need to have a panel that gets IGN power, not straight battery, then wire a relay into the IGN circuit - the radio circuit is a nice one to use as it usually doesn't draw much power - that adds only milli-amps of current draw to the existing circuit to switch battery power to the aux panel when IGN is on.  Make sure the relay you use is rated for at least the total load of fuses you'll put in that aux panel.

2- It wouldn't surprise me if the headlights alone are heating up the fuse panel (and other things).  This is why I stated 1 above first.  I always recommend older Gs especially convert to a headlamp relay system, regardless of whether they want to fit up-rated bulbs or not.  Daniel Stern gives a good description here: http://www.danielsternlighting.com/tech/relays/relays.html  and easy to wire kits are available here: http://www.shopatron.com/product/product_id=PPF30815/302.0 In my opinion, although the $ sounds like a lot, an easy to install, properly designed and rated system like the one from Painless is worth the money 10 times over in the amount of future pain it will save you.  If you haven't already had to replace your multi-function turn signal stalk and/or headlight switch, this kit may even save you the hundreds of dollars involved in those repairs.  Yes, you can put together a relay system for less money, but if you try to put together one as good as the Painless one, with high quality water sealed relays and connections, the proper gauge wires everywhere, etc, you won't save $20.  That said, the only thing I wish Painless had done differently was I wish they'd used full length tinned marine grade wire in the harness.  If they'd done that, they'd have it all.  As it is, I haven't found any corrosion in the wiring of any of the Painless systems I've used on the one or two occaisions I've had to open them up, so any difference may not be visible for 20-30 years anyway.

If you go to CGW Gtech, my article on headlight switch repair shows some of the long term effects of the factory designed headlight wiring.

-Dave G.