Your poncirus trifoliata rootstock
should add about 5F cold hardiness to each variety of lemons you have. that should take your Eureka lemon down to the low 20s-F and your Meyer lemon down to the high teens-F. You will need to be prepared to provide 25F heat rise to keep your trees alive for a once in 10-20 year cold snap. Lemons grow fast so you'll do better if you can grow them on their own roots to a bud node count of 75 or greater, 5-7 feet tall, before grafting. On PT the grafted bud will grow with closer bud nodes and should reach fruit producing maturity around 2-3 feet tall. a 5 foot tall tree is a lot easier to protect than a 9-10 foot tall tree. The Meyer lemon will not grow true to seed and will taste different but possibly quit good.
I am using mine to plant a hedge row on my property.