Yes I use I2P with split setup. My setup is as follows:
- Use VPN that supports external port forwarding
- Configure qubes-tunnel with port forwarding from “sys-vpn” to “sys-i2p”. Now I2P should have full connectivity.
- Configure I2P to accept client connections from qubes network interface rather than from localhost
- Use sys-i2p as network VM for i2p AppVM
- Use local IP of sys-i2p as HTTP proxy in Firefox in the i2p AppVM
Now the i2p AppVM can directly access the IP address of sys-i2p as a HTTP proxy because it is configured as the upstream network VM, so everything works nicely.
Everything in the AppVM that does not have a HTTP proxy configured will bypass I2P and will be routed via the VPN instead. Which is kinda meh in terms of anonymity but should be easy to suppress if necessary.
I just installed I2P in a Qubes Debian 10 template with sudo apt-get install i2p
IIRC the Debian version of I2P is very outdated, you should probably follow the guide here Debian/Ubuntu - I2P