Hi. Sorry to hear about the refusal.
At the risk of stating the obvious, surely the best way for your other half to prove that he can support you without recourse to public funds once married, is to already be supporting you - and have proof of this - Western union receipts etc etc....They cant say he cannot support you if he is already doing so successfully.
I stated in my sponsor's letter that i had visited the Phils 5 times in 4 months at a cost of xxx and supported my wife to the tune of xxxx per month, and that this would obviously equate to a significant disposable income once my wife was with me.
Going over an 'agreed' overdraft shows poor financial management and could also be misconstrued as a lack of respect for rules and regualtions. (I would imagine that 30 x bank fees plus interest and letter charges- peppered throughout his bank statements - looks like a cause for concern despite the small amount ). Why not increase the agreed overdraft? If he only goes £150 into an agreed £300 overdraft with no fees he is not doing anything untoward. Why not have a spring clean and sell £150 worth of junk on ebay and get himself out of the overdraft? Where theres a will theres a way!
