X2 on Scripts Poway Parkway being the easiest.
Now North of Santa Ysabel on 79 you turn R onto S2 (San Felipe Road).
Then a few miles down the road turn L onto S22 to Borrego Springs. Do not miss that turn and continue on down to 78.
That turn onto S22 will take you thru Ranchita down the Montezuma Grade into Borrego Springs.
(On edit) I just noticed that you have previously gone into Borrego across Yaqui Pass on S3. That's a tough way in. On some of the curves you are out into the downhill traffic lane on a very narrow road.
RV parks in Borrego Springs recommend the Montezuma Grade as a preferred way in for those coming from the west. It's hardly more than an interstate highway grade. And with a beautiful view of the valley most of the way down.