A few questions, to understand your setup a little better. When you say…
I have a mono series run of pedals until I get to the Strymon deco as that goes out stereo to my amps inputs.
Are you running your amps completely clean and letting your pedals provide the tone shaping for you? Are you using the FX loops at all?
How can I run dual routing with the Deco’s left and right into the H90 and then have the wet effects in the loop of the amp. Do I run the Deco’s stereo out left and right into the H90’s In 1 and In 2, then out 3 and out 4 to send and return (which is which, if possible).
Yes, you can go from the Deco to the H90 in stereo, but when using Dual Routing mode, the idea is you connect one path to the input of your amps and the other path to the FX loops of your amps. In order to put Eventide algorithms in the amps’ FX loops, you’ll have to send the signal from the amps’ FX send to your Deco, then take the signal to In 3&4 of the H90 and go from Out 3&4 of the H90 back to the FX returns. Isolation transformers on one side of send and returns are highly recommended to prevent ground loops.
I also want to be able to use the weedwacker and other awesome Algo’s but can that be done in dual routing when you have other drives and fuzz and modulations on your board?
By connecting your guitar to the H90 on In 1 and taking Out 1 and Out 2 to the front of your amps, you can now place Weedwacker on Path 1, which will be signal headed to the input of your amps. Any other gain-based effects can be placed before the input of the H90.