How do you calculate this premium? Is it just for stocks that replicate BTC price, or also for highly correlated mining stocks? Would it make any sense to compare this premiums with mining stocks? I am long Argo blockchain, LSE, for bitcoin play, seems undervalued compared to its sector. Also have an option play on Riot but I feel this stock is overvalued. Crypto wise I have a buy and forget paper wallet basket that I built using coinbase and binance, and myetherwallet. I wish I built this at the time I was playing around with anonymous btc-e exchange when bitcoin was a 300$...
A "regular" bitcoin exchange should let you transfer the coin to any wallet of your choice. A bit like with stocks Vs CFD. Binance, kraken, coinbase... You own the code and do what you like with it. Brokers who offer trading with it, like a CFD, might have their own reserves but you can only trade it like a CFD, no transfers or withdrawal of the coin/token itself.
Or you could just trade a proxy: https://www.elitetrader.com/et/threads/best-bitcoin-proxy-to-trade-mstr.354694/page-3#post-5318180
You calculate the premium by adding 3 zeros to GBTC and comparing to BTC on Coinbase or any other exchange. Incidentally at the peak in 2017 GBTC got to a 100% premium. It traded at 38 when BTC was 19,000. Back then people were not as aware as how to buy Bitcoin so this was the easy way to do it. Poor fools not only lost when Bitcoin came down they had a double loss when the premium evaporated.