While not being 100% how I would fit it… this will do…
If you make that unbumpable in bastion mode, you just switch the MJD with an MWD to counter a possible bump attempts while playing station games or hugging a gate.
In Bastion Mode with drugs alone (not even using asklepians) that thing will tank round about 4k (almost 5K while overheating) dps until it runs out of cap charges.
With bastion being inactive it still is tanking close to 2K dps and even if you manage to neutralize it´s capacitor by the time it drops out of bastion it still has 81k+ EHP. Having a cap booster fitted however it still will be able to repair a cycle here and there. A single cycle is round about 40K EHP added.
At the same time it can potentially hurl 1.5K dps into your direction (I ll go into why that matters further down).
So… assume you engage that near a Station. He sits unbumpable right at the undocking point. While he is in Bastion mode you need to have 5 ships with 1K dps+ (as if that is not broken enough already…).
In other words… you are not ever going to break his tank, while he is sitting there in bastion mode, without neuting has capacitor completly dry.
As soon as he notices that this is your game plan (which will already be quite obvious by your the choice of the ship you engage him with in the first place), he turns his basion module red, disengages his turrets and starts cap boosting and keeps his armor topped up. Which with the repair amount in bastion mode is not going to take a lot of cycles and won´t be very heavy on his capacitor. He can pretty much just sit there and while his capacitor goes down, He just needs to pulse his cap booster 2x and his rep 2 times to fully repair his armor 2 times, which is already 2x as much as any single subcapital ship will deal in the maximum timeframe of 60 seconds until his bastion module turns off.
So now Bastion goes inactive and he becomes bumpable. By now he already reloaded his cap booster and has 5 x 800 cap available and still has easily 60K EHP left for you to chew through at full armor.
Now you have 60 seconds to push out of docking range, while he can as well pulse his cap booster and MWD to counter your bump and pulse his repairer once. And unless being completly incompetent will happily sit out the 60 seconds until he can dock, being perfectly able to maintain in range.
So to defeat him you would a) need to completly neutralize his cap b) deal at the very list 1K dps and have a ship with enough mass and velocity to give him a proper bump, to get him outside of docking range. c) You need to be able to tank 1.5K DPS yourself or he will shred you into pieces.
Keep in mind if it looks like you could possibly get a good enough bump in, he always also has the option to activate the bastion module again and to try to counter you again. A minute later.
Now with the current way bastion works. After engaging him you have time to start pushing him out of docking range, before his bastion module goes inactive, with no option for him to dodge / counter your bump attempt, which is pretty much your only hope of killing him, with anything but a completly overwhelming force.
But you can not balance ships around the possibility of 1 v X scenarios, even if 1 v 1s are not that common, and as powerful as marauders already are, your only hope is bumping them out of range or dropping at least enough ships to deal round about 5K dps to drop him before he can dock.
This kind of reckless power creep is one of the things that over the years has made PvP in EvE so dull and only leads further away from strategical fights to boring N+1 fights.
This is already totally broken. And making them unbumpable in bastion mode will only add to that already way overpoweredness.