Beefing up 240D suspension

[10fords]

As the price of fuel has skyrocketed in my area ($4.59 gal yesterday) I have been using my 81 240D a lot more for work, and leaving the F350 at home. While the trunk has an amazing amount of space the suspension is struggling with the weight of all my tools and parts! Does anyone know of a way to add some capacity to the suspension? I notice that in the FSM there is a variety of spring applications for bad roads, taxis, etc. As I doubt I can get new springs from the dealer for a 30 yr old car is there a donor vehicle I should look for for some heavier springs? From a wagon perhaps? Can I add some taller spring pads as well? As usual any advice is greatly appreciated- Scott