Let's say your weekly DCA is $50 and you know that withdrawal fee will be needed you can make it $55 and use the $5 to cover the fee.
I don't think it is a smart move to use 10% of your capital as withdrawal fee, that is too high for me. Instead of doing that, you could buy weekly but withdraw monthly, this way you will be cutting down the fee to 2.5% of your capital. If you continue to spend $5 as withdrawal fee for a $50 weekly DCA, that will amount to $260 annually as fee which is too high for such a low capital. So lile I said before, instead of this, a weeklg DCA and monthly withdrawal will be better.
What I'm suggesting to you is also what I'm doing because we have to maximise the opportunities while cutting down the cost of doing that.
If you read my post carefully you will understand that I said the $5 addition is just something you are adding up to make up for your withdrawal fee and I also made mention that you shouldn't withdrawal weekly unless you are buying up to $200 and above. If you buy $50 weekly you have to leave it till it gets to like $200 which is up to 4 weeks making it a month. So if you are adding the $5 for that 4 weeks you are likely going to have $220 so when you are withdrawing the withdrawal fees will be charged from the extra money you added to your initial weekly allowance for DCA, the fee might not get to the $20 depending on the exchange and their charges, there is every possibility that the extra $20 won't be exhausted on the withdrawal fees so the rest will still go to your holding. The essence of this is to make sure that your weekly DCA target is not shorten because of exchange fees. The choice of how many times to withdraw to a non custodian wallet solely lies with the investor, if he chooses to do it weekly if he can afford the fees that's fine, but if he can't he can do it monthly as you have stated above. But the most important thing is to get our assets off custodian wallets. We can't take because of withdrawal fees and lose our bitcoin.