Bolting On Heater Bubble

Obvious rust spot. Thinking of bolting on so that leaves can be removed over time and fresh sealer applied.
Has anybody done this?? Not sure how much, if at all, of a problem leakage will be around holes? I am thinking of using fibre or rubber washers or welding the nuts under the dash all the way round (might be too fiddly).
Comments???
Has anybody done this?? Not sure how much, if at all, of a problem leakage will be around holes? I am thinking of using fibre or rubber washers or welding the nuts under the dash all the way round (might be too fiddly).
Comments???