If you have enough money to invest then you can invest. If you don't like the market at the moment then you can continue using the DCA method because investing in the DCA method will give you a better investment method and you will have a higher chance of success. But you can use electum wallet or trust wallet to hold the investment but the wallet seed must be kept very safe.
I wouldn't recommend Trustwallet.
https://bitcointalk.org/index.php?topic=5420819.msg61284073#msg61284073A thread that showed Trustwallet isn't open source nor really decentralized ever since it was acquired by Binance.
I have been using trustwallet for quite some time but to be honest, it is not the most recommended wallet for newbies and even for those who are no longer a newbie.
I'm surprised you still use it despite knowing its closed sourced or maybe it's used for Pocket change
Still don't see how that is any different from using CEX.