Joe, Thanks, the web site was particularly useful! I have no access tot he top of any of the tanks but it sounds like a side mount will work according to their installation instructions - however I need to think about a side mount on the fuel tanks - don't want to risk a leak...... Mike - > How easy is the "tank tender" to install? Does it work well on holding > tanks? Are they sold by West Marine or Boat US? What would it cost to buy a > system to monitor 6 tanks (2 fuel, 2 water and 2 holding)? I believe you will need a 10 tank unit for 6 tanks - installation consists of mounting thee gauge/pump unit and then running 6 1/8 inch nylon tubes to each tank - you need access to the top of the tank for a small fitting - a tube then goes to the bottom of each tank - what you actually measure is the column of liquid in each tube for reference.... it works very well I have used it on sailboats to monitor all of the tanks....check out this link: http://www.progress.fr/uk/tanktender.html You sould be order from West or Boat US via special order service - do not know current costs. Joe Urban Trawlerless in VA