Another option which you many not have considered is to use a segmented dipole rather than
a parallel dipole. The advantage is that you have no interaction between bands with the segmented dipole and it is easier to tune.
Each leg is made up of a single wire that is broken into segments by insulators that can be bridged using jumpers. The idea is the two wire lengths attached to the center insulator form a resonant dipole at the highest band of operation. Jumpers are then used to bridge the end insulators to add-on an extra bit of wire on each end of the dipole that will make the antenna resonate on the next lowest band. This is repeated to cover as many bands as desired. The idea is similar to a trap dipole except instead of traps you are manually connecting extra wire on the end of each leg to resonate it on a lower band.
This becomes a bit cumbersome when have too many bands but it works well for a few
if you don't mind lowering the antenna to move clip-leads. It is great for portable QRP operation as it can be made out of lightweight wire and requires no tuner for multi-band coverage (each added on section makes the antenna resonant for the next lowest band).
A picture is worth a thousand words so I will refer you to WA3WSJ's excellent write up on this antenna :http://wa3wsj.homestead.com/iditarod_mini__dipole.pdf
P.S. I can't say who came up with this idea originally but I remember an article in CQ Magazine
dating back to the late 1970's.
P.P.S. Mine is made out of #24 AWG Teflon coated, silver plated wire and covers 40m/30m/20m which is perfect for use with my Elecraft KX1.