generally marine interior fabric meets the same anti-microbial requirements of outdoor fabric. however doesn't have the UV stability of outdoor fabric.
sunbrella is one of the many marine upholstery companies
you have to judge for yourself, your boat, your skills, the geography of your surroundings, etc.
for example, a 40km/hr gust in one location may simply knock your hat off, in other locations it may cause 1.5-2 meter swells
the cost of new and reman is higher than the higher volume V6's and V8's which started life as truck engines as this engine is a GM industrial engine and is only used in trash pumps, fork lifts and entry level boats.
welcome aboard.
since you have a cottage, my recommendation is a pair of jet skis, a pontoon boat, keep the fishing boat, and also get a few kayaks.
to have a bunch of people in the boat to slowly tour the lake - pontoon boat
to go fishing - fishing boat
for water sports - jet ski
for quiet...
what is the shape of your tank? is it fairly shallow and under the floor? bow mounted? stern mounted?
what angle does your boat sit at while static? on-plane?
I know of many shallow, below deck tanks that dont read worth a carp because they are long, and shallow and the boat sits at enough...
Im sure glad these are your friends. coils almost never need to be replaced. only 3 out of a million changed coils are actually bad. did they do any troubleshooting?
what else was replaced that didnt need to be replaced?
since the motors have not changed much from 1991 on, look for a trashed boat with a good motor.
I would do a leak down test to determine if its rings or valves or what. could just need a head job
however Reserector also has a good point. you may want to try some of the decarboning solutions...
been spraying, sanding and buffing for longer than care to admit
the 400 grit to 1500 grit has been my ticket for decades. everything from old hulls to new gel jobs. I used to wet sand by hand, however I no longer have that kind of time.