I bit the bullet and drained the tank and opened it up today. This was very informative.
I emptied the tank by running the electric fuel pump and pumping into 5 gal cans. It was able to suck it right down to the bottom, leaving only about a cup of fuel.
1. My access port is about 6" square secured with 8 machine screws tapped into the tank top and sealed with some sort of sealant. The sealant was hard and poorly adhering so that the plate just lifted right off. No doubt this would leak if the tank were over filled, accounting for the diesel I once found in the bilge.
2. When the access port was installed, some of the squeezed out into the tank. Most of it was stuck to the sides, but a few drips on the bottom of the tank hadn't stuck and were floating around waiting to plug the intake line.
3. The tank was remarkably clean. There was a little sludge in places on the bottom totaling maybe 5 sq in. in spots about the size a quarter. The fuel level sensor is quite clean. Cleaning it looks to be a relatively easy job if I put in another access plate on the port side.
4. There is one baffle running front to back from top to bottom with the bottom corner cut off on the pickup end. There is no way to get past this baffle to clean the port side or even inspect it, without installing another access plate.
5. Without any lateral baffling, it still seems to me that sucking air in rough conditions is a big concern, I'm thinking I don't have to worry too much until I get down to the last 5 gallons or so.