To clarify, when you say it catches sometimes, do you mean it starts sometimes or it cranks sometimes?
The starting system is to most basic system in the entire vehicle. It has a battery, battery cables, a solenoid and a starter. The ground cable needs to be grounded to the block and to the frame or body to make a complete circuit.
I would try cranking it by jumping the solenoid. It is possible for a worn out key switch to cause cranking issues.
If the problem is in fact heat related, it could be an old starter going bad. It could also be that the cables are just junk. Old cables go bad from heat and corrosion. They should be a minimum of 4ga, but 2ga is better. If the terminals are the screw on variety, with the two 10mm or 7/16 head bolts clamping the frayed cable to the terminal, those are horrible as there is virtually no protection against corrosion where the cable makes the connection.