Diesel Engines....Help....?

I don't know if this is the right place to ask, but you guys are such a help.... I have a 16 foot diesel cube van... and I got a new set of homes to build which is really far. I am getting crappy mileage... I have changed the fuel filter and do regular 5000 kilometre oil changes. It costs me about $120.00 Canadian a tankful (about 140 litres) I drive it for work, and usually have to fill it up every 2 days... which really sucks. I don't really care about this truck, but I want to get some more bang for buck, if you know what I mean. I heard that if you use Amsoil synthetic oil...that you could get about 8 - 10 % increase in fuel mileage... but when you have 20 litres of oil in this beast that gets a bit $$$$$$$$! So I was thinking what if I got some plastic pipes like what the plumbers use.... and maybe cut a hole at the bottom of the air intake system and create my own air intake system from those pipes? What do you guys think? Do you think I could get some fuel improvements.... Any other ideas? Cheap ideas? Please help... my pockets are getting lighter day by day....

if its turbo charged have your intercooler and the system checked for air leaks,this will cause terrible milage on a deisel..jj