Running 4 GA Power wire on frame, Pros And Cons?

[NICE59FORDF100]

Well,First of all, i got an awesome deal on some 4 gauge wire off ebay, basically paying $1.11 a foot:

red 4 gauge wire

now, im going to be using this wire to go from a battery isolator to an aux battery that will be located in the passenger quater panel. Heres my question: What are the pros and cons of running a power wire that size along the frame rail, albeit in red 1/2 inch wire loom zip tied the frame to hold it in place?

 

[BrooklynBay]

I like to run this in Watertite gray conduit. I think it's safer, but this is just my opinion.

 

[vrytired]

i ran my #4 wire just as you say, ziptieing it around/about frame. i've got a 60 amp fuse 10 in from the battery so i'm not to worried about shorts. got my wire at walmart for .50 a foot. saw some 20 foot long #4 ga jumper cables for 20 bucks, cheap wire.