you can do your stop loss at $40k and make a DCA at $30k. Stop loss first and wait for price falls deeper to make DCA. So if you want to apply this, you have to do stop-loss early enough so that you can wait for deeper falls which would be -20% from your stop-loss price. At which you will have a new entry, for DCA.
After exiting at $40k by hitting stoploss, then with what position that you are going to average at $30k levels? In my understanding, averaging will be possible only if you have open trades. It is even applicable for investments. If you exit all your holding then entering again will be considered "buy back" not averaging.
So, trying to making use of DCA along with stoploss will not provide the actual benefit of DCA.
A very basic thing on which you shouldnt put up stop loss because once it do triggers out then those losses are realized unlike if those are open orders then you could really able to apply averaging
and this is how DCA been performed and to those people who do believed about applying SL on DCA method then it couldnt really be just possible because this isnt how should be applied.
On the side note of DCA then this one sounds very basic and simply but this would test out your emotion and of course your capital on doing so.