I was wondering if there would be any problem replacing the fiberglass tubing in the exhaust with stainless?

where do you have fiberglass tubing in your exhaust? I cant imagine there would be any prob going with all SS, thats the way it should be anyway.

It goes from my risers to my side exhaust. Right now there is even a big fiberglass muffler. But I see the elbows are cracked. My buddies boat has basically the same setup but no mufflers. I was just wondering if the fiberglass was used to keep heat down in the engine bay or anything? And if the stainless would cause any problems

Will just add a little weight, but won't have to worry about them cracking. My Pachanga had the same setup as yours, but had the AL elbows.

I would think it wouldn't be too bad for weight if I used a tubing like exhaust tubing in trucks

Try to get 316 or (better yet) 316L stainless. Typical 304 stainless is not as corrosion resistant as you might think. Stainless Marine (Google them) could probably supply whatever you need.

Remember - a leak in a wet exhaust system can sink your boat.

What about maybe using aluminum?

I would go straight to the 316L SS and don't bother with the aluminum. It will eventually corrode, even in fresh water. The calcium, magnesium, etc. in fresh water will eat up the aluminum exhaust tubing. Once you do it with SS, you will never have to worry about it again.
Eddie

Has anyone done this and have an idea of what the cost would be?

I whats the headers made of 316 or 304 theres some companys that use one for headers and the other for there tails. so which is a better ss 304 or 316. I will go to the web sites see who uses what.