i have a procraft 20 ft bass boat that i would like to tow my wife and kid on one of those inner tube tow behind deals.  just for a few days next summer.  is there anywhere on the boat that can support this weight to tie off to?   also what about some kind of a throw over ladder to get in and out of the boat.

You can buy those ladders i would check cabelas or basspro shops

We water ski and tube behind my old mans bass boat.  We just tie the rope to the trailer loops off the back.  You can get a small float that keeps the rope out of the motor better too.  But it works great.  The 20' foot boat shouldnt be pulled too badly by the skiier.

Use the transom tiedown eyes on the back, make sure you use one of those ski bridles.  OR  You can get fancy and spend around $120-150 and get a pylon. One end fits into the rear pedestal base and the other two to attachments that you have to mount to the boat.  No bridle needed then.  

As for a ladder, I used one of those 4 step hang over the side deals for years and it worked great.

I've skied bunches of miles behind bass boats and pulled bunches of skiers.  As cart7 mentioned, they make tow strap that goes across the back of the boat and hooks into each of the tie-down eyes.  It has a hook/eye to hook your ski rope and a float on it to help keep it from getting down into the prop.   Works great.

Getting in and out of the boat, just stand on the anticav plate or back of the mid section where it goes out to the lower unit, trim the motor up and step over into the boat or get one of those ladders you can flip over into the water.